Assuming that the Godfather, Part II is not an acceptable answer, I would say that Scarface is probably the next best mob movie (to the extent that it is a mob movie, in that it does not focus on...
A horror movie about a horror movie is almost certainly Terror in the Aisles (1984), which is a horror-documentary narrated by Donald Pleasence, who starred in Halloween (1978), and Nancy Allen, who...